Railroads are typically constructed to include a pair of elongated, substantially parallel rails, which are coupled to a plurality of laterally extending rail ties. The rail ties are disposed on a ballast bed of hard particulate material such as gravel and are used to support the rails. Over time, normal wear and tear on the railroad may cause the rails to deviate from a desired profile based on movement of the underlying ballast, and as such voids or gaps under the rail ties may appear.
The traditional method of fixing voids that appeared under rail ties was very labor and time intensive, as it required measurement of the voids under each individual rail tie, manually lifting the rail ties, and then spreading a pre-measured quantity of ballast under the rail ties to raise the rails. In the 1970s, British Rail developed a mechanization of the traditional method by modifying a tamper and installing a system for distributing ballast under the rail tie with blasts of compressed air, creating the first stoneblower.
Modern stoneblowers are typically wheeled cars that comprise a track lifting device, a supply of crushed ballast rock, a source of compressed air, and a number of workheads. Each workhead carries a pair of blowing tubes. In operation, the track lifting device raises the track rails and the underlying rail ties to which the rails are secured. The workhead forces the blowing tubes into the ballast adjacent the raised rail ties with each pair of blowing tubes straddling a track rail. Stone is then blown through the blowing tubes into the voids beneath the raised rail ties. The workhead withdraws the blowing tubes and the track rail and rail ties are lowered. The stoneblower then advances to the next set of rail ties and repeats this procedure.
Modern stoneblowers are designed to restore a track's vertical and lateral alignment to an accuracy of 1.0 mm without disturbing the pre-existing compacted ballast layer. Vehicle bogies allow stoneblowers to measure a loaded track profile, and therefore measure the voids in the ballast under each rail tie. Computers then calculate the quantity of ballast to be “blown” under each rail tie to properly align the rail.
Compared with tamping, stoneblowers advantageously can be used on high speed track lines, treat only the areas of the track that need treatment, and reduce ballast damage. Further, after stoneblowing, the track does not become more rigid because the stoneblower only treats areas that need treatment, while the majority of the rail ties are supported on the original ballast and railroad bed. In addition, a new rock supplier is not needed to use a stoneblower for track maintenance. The injected ballast often comes from the same quarries and has the same attrition values as normal ballast. Additionally, using small, crushed stones as ballast causes less damage to the underside of the rail ties because the small stone is less likely to fail under heavy axle load based on increased surface area.
Stoneblowers have some drawbacks, however, based on the current rail-bound design. For example, modern stoneblowers struggle to blow ballast under sections of rails near various fixed structures such as bridges and overpasses. That is, conventional stoneblowers are arranged with the jacking mechanism positioned forward of the blowing tubes. When conventional stoneblowers approach a fixed structure, such as a bridge, such machines are capable of adequately blowing ballast adjacent to the fixed structure in a first direction, but cannot adequately blow ballast adjacent to the fixed structure at the opposite side of the fixed structure due to the positioning of the blowing tubes and jacking mechanism. This is because the jacking mechanism is unable to lift the fixed structure in order to blow ballast underneath a tie located adjacent to the fixed structure.
In the continually changing world of track maintenance, it is essential that rail companies be able to provide quality track maintenance and alignment equipment that can service all sections of rail, including sections of rail adjacent to fixed structures. Further, what is needed is a stoneblower that is agile and more efficient than standard rail-bound stoneblowers. Therefore, an improved stoneblower is desired.